The "Comparative Indicators of Education" report series has been published on a biennial basis since it began in 2002, although this year's is the first to expand its focus to the G-20 countries, having previously been focused on the G-8 countries. "Comparative Indicators of Education in the United States and Other G-20 Countries: 2015" is a comparison of the education system in the United States with those in the other Group of 20 (G-20) countries: Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, the Republic of Korea, the Russian Federation, Saudi Arabia, South Africa, Turkey, and the United Kingdom. The G-20 countries, which are among the most economically developed, represent 85 percent of the world's economy and two-thirds of its population. These countries are some of the United States' largest economic partners. The report draws on the most current information about education from the International Indicators of Education Systems (INES) project at the Organization for Economic Cooperation and Development (OECD), as reported in the "Education at a Glance" series, as well as international assessments that range from grade 4 through adulthood. These international assessments include the Progress in International Reading Literacy Study (PIRLS), which assesses fourth-graders in reading; the Trends in International Mathematics and Science Study (TIMSS), which assesses fourth- and eighth-graders in mathematics and science; the Program for International Student Assessment (PISA), which assesses 15-year-old students (regardless of grade) in mathematics, reading, science, and, occasionally, other subjects; and the Program for the International Assessment of Adult Competencies (PIAAC), which assesses adults, ages 16 to 65, in literacy, numeracy, and problem solving in technology-rich environments. Findings are organized into five major sections: (1) population and school enrollment; (2) academic performance; (3) contexts for learning; (4) expenditure for education; and (5) education returns: educational attainment and income. An appendix presents: The Education Systems of the G-20 Countries.